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The Single UNIX &reg; Specification, Version 2<br>
Copyright &copy; 1997 The Open Group

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<h4><a name = "tag_000_007_808">&nbsp;</a>NAME</h4><blockquote>
msgget - get the message queue identifier
</blockquote><h4><a name = "tag_000_007_809">&nbsp;</a>SYNOPSIS</h4><blockquote>
<pre><code>

#include &lt;<a href="sysmsg.h.html">sys/msg.h</a>&gt;

int msgget(key_t <i>key</i>, int <i>msgflg</i>);
</code>
</pre>
</blockquote><h4><a name = "tag_000_007_810">&nbsp;</a>DESCRIPTION</h4><blockquote>
The
<i>msgget()</i>
function returns the message queue identifier associated with the argument
<i>key</i>.
<p>
A message queue identifier, associated message queue and data structure,
see
<i><a href="sysmsg.h.html">&lt;sys/msg.h&gt;</a></i>,
are created for the argument
<i>key</i>
if one of the following is true:
<ul>
<p>
<li>
The argument
<i>key</i>
is equal to IPC_PRIVATE.
<p>
<li>
The argument
<i>key</i>
does not already have a message queue identifier
associated with it, and (<i>msgflg</i> &amp; IPC_CREAT) is non-zero.
<p>
</ul>
<p>
Upon creation, the data structure associated with
the new message queue identifier is initialised as follows:
<ul>
<p>
<li>
<b>msg_perm.cuid</b>,
<b>msg_perm.uid</b>,
<b>msg_perm.cgid</b>
and
<b>msg_perm.gid</b>
are set equal to the effective user ID
and effective group ID, respectively, of the calling process.
<p>
<li>
The low-order 9 bits of
<b>msg_perm.mode</b>
are set equal to the low-order 9 bits of
<i>msgflg</i>.
<p>
<li>
<b>msg_qnum</b>,
<b>msg_lspid</b>,
<b>msg_lrpid</b>,
<b>msg_stime</b>
and
<b>msg_rtime</b>
are set equal to 0.
<p>
<li>
<b>msg_ctime</b>
is set equal to the current time.
<p>
<li>
<b>msg_qbytes</b>
is set equal to the system limit.
<p>
</ul>
</blockquote><h4><a name = "tag_000_007_811">&nbsp;</a>RETURN VALUE</h4><blockquote>
Upon successful completion,
<i>msgget()</i>
returns a non-negative integer,
namely a message queue identifier.  Otherwise, it returns -1 and
<i>errno</i>
is set to indicate the error.
</blockquote><h4><a name = "tag_000_007_812">&nbsp;</a>ERRORS</h4><blockquote>
The
<i>msgget()</i>
function will fail if:
<dl compact>

<dt>[EACCES]<dd>
A message queue identifier exists for the argument
<i>key</i>,
but operation permission
as specified by the low-order 9 bits of
<i>msgflg</i>
would not be granted, see
<a href="ipc.html">IPC</a>.

<dt>[EEXIST]<dd>
A message queue identifier exists for the argument
<i>key</i>
but ((<i>msgflg</i> &amp; IPC_CREAT) &amp;&amp; (<i>msgflg</i> &amp; IPC_EXCL)) is non-zero.

<dt>[ENOENT]<dd>
A message queue identifier does not exist for the argument
<i>key</i>
and (<i>msgflg</i> &amp; IPC_CREAT) is 0.

<dt>[ENOSPC]<dd>
A message queue identifier is to be created but the
system-imposed limit on the maximum number of allowed
message queue identifiers system-wide would be exceeded.

</dl>
</blockquote><h4><a name = "tag_000_007_813">&nbsp;</a>EXAMPLES</h4><blockquote>
None.
</blockquote><h4><a name = "tag_000_007_814">&nbsp;</a>APPLICATION USAGE</h4><blockquote>
The POSIX Realtime Extension defines alternative interfaces for interprocess communication.
Application developers who need to use IPC should design their
applications so that modules using the IPC routines described in
<a href="ipc.html">IPC</a>
can be easily modified to use the alternative interfaces.
</blockquote><h4><a name = "tag_000_007_815">&nbsp;</a>FUTURE DIRECTIONS</h4><blockquote>
None.
</blockquote><h4><a name = "tag_000_007_816">&nbsp;</a>SEE ALSO</h4><blockquote>
<i><a href="mq_close.html">mq_close()</a></i>,
<i><a href="mq_getattr.html">mq_getattr()</a></i>,
<i><a href="mq_notify.html">mq_notify()</a></i>,
<i><a href="mq_open.html">mq_open()</a></i>,
<i><a href="mq_receive.html">mq_receive()</a></i>,
<i><a href="mq_send.html">mq_send()</a></i>,
<i><a href="mq_setattr.html">mq_setattr()</a></i>,
<i><a href="mq_unlink.html">mq_unlink()</a></i>,
<i><a href="msgctl.html">msgctl()</a></i>,
<i><a href="msgrcv.html">msgrcv()</a></i>,
<i><a href="msgsnd.html">msgsnd()</a></i>,
<i><a href="sysmsg.h.html">&lt;sys/msg.h&gt;</a></i>,
<a href="ipc.html">IPC</a>.
</blockquote><h4>DERIVATION</h4><blockquote>
Derived from Issue 2 of the SVID.
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UNIX &reg; is a registered Trademark of The Open Group.<br>
Copyright &copy; 1997 The Open Group
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